Lockable latch mechanisms are used in vehicles and can be in an unlocked condition (i.e., allowing opening of an associated door from the outside and from the inside), a locked condition (i.e., preventing opening of the door from the outside but allowing opening of the door from the inside), and a superlocked condition (i.e., preventing opening of the door from both the inside and the outside).
European Patent Application EP 01303421 discloses a lock mechanism operable from the inside of a vehicle by a sill button or toggle switch. The sill button is connected to the lock mechanism via a coil bound helical spring. This spring acts in a non-resilient manner when the sill button is subsequently operated to move the lock mechanism between the locked and unlocked conditions. When the lock mechanism is electrically driven to the superlocked condition, the helical spring prevents the sill button from actuating the lock mechanism by acting in a resilient manner when the sill button is operated in an attempt to move the lock mechanism from the superlocked condition.
However, if the vehicle is involved in a collision, there may be sufficient damage to the lock mechanism to cause the lock mechanism to partially seize. If the lock mechanism were locked at the time of the collision, exit from the vehicle may be impeded because the helical spring may elastically deform rather than transmitting sufficient force to the lock mechanism to unlock the lock mechanism. In such circumstances, it would be very difficult to unlock the door from the inside of the vehicle.
An object of the present invention is to provide an improved lock mechanism that overcomes these deficiencies.